Finite extensible nonlinear elastic potential FENE

The Gaussian bond (1.4) can easily be stretched to high extension, and allows unphysical mutual passing of bonds. To prevent this unreaUstic mechanical property, the model potential, called the finitely extensible nonlinear elastic potential (FENE), and described by... 

Figure 1.41. Potential energies for the bead-spring model LJ1—Lennard-Jones potential LJ2—van der Waals potential EXP1, EXP2—short-range polar potential FENE—finitely extensible nonlinear elastic potential.

LJl) and van der Waals (LJ2) potentials were used for nonpolar bead-bead and bead-wall interactions, respectively. For polar interactions, exponential potential functions (EXP 1,2) were added to both bead-bead and bead-wall cases. For the bonding potential between adjacent beads in the chain, a finitely extensible nonlinear elastic (FENE) model was used. For example, PFPE Zdol... 

The bond potential within the confinement region r,, + — ro < R (the total symmetric fluctuation width is 2R and centered about ro) is typically modeled by the finitely extensible nonlinear elastic (FENE) potential [50], which we introduce here in the form [51]... 

The mesoscale model consists of a set of crosslink nodes (i.e., junctions) connected via single finite-extensible nonlinear elastic (FENE) bonds (that can be potentially cross-linked and/or scissioned), which represent the chain segments between crosslinks. In addition, there is a repulsive Lennard-Jones interaction between all crosslink positions to simulate volume exclusion effects. The Eennard-Jones and FENE interaction parameters were adjusted and the degree of polymerization (p) for a given length of a FENE bond calibrated until the MWD computed from our network matched the experimental MWD of the virgin material [112]. 

The (two-dimensional) model for a relatively stiff molecule subjected to a simple shear flow, on the one hand, shows many features observed in NEMD simulations of finitely extendible nonlinear elastic (FENE) chain molecules. On the other hand, the dynamics found for the simple model is intriguingly complex and it deserved a careful study on its own. It seems appropriate also to analyse the system at higher temperatures. Furthermore, the model provides a convenient test bed for various thermostats other and additional thermostats, e.g. based on deterministic scattering [22] should be tested. Obvious extensions of the present model may involve other potential functions of nonlinear elastic type such as = (1/2) -I- (1/4) or = (1/4) (1 — r ) as well as... 

The simulation techniques used for polyelectrolytes in solution are extensions of the standard methods used for neutral polymers. The polymer chain is modeled as a set of connected beads. The beads are charged depending on the charge fraction, but otherwise the details of the monomer structure are neglected. Various means of connecting the bonded monomers are used. In lattice Monte Carlo the bonds are of course fixed. Two sets of simulations have used the rotational isomeric state model. Other simulations have used Hookean springs or the finite-extendable-nonlinear-elastic (FENE) potential. No important dependence on the nature of the bonds is expected at this level of modeling the polymer chain. 

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